In general I do not approve of feeding an animal a diet so radically different from its natural diet. The digestive systems of dogs and cats are very different from those of herbivorous animals, and they simply do not process plant matter as well.

HOWEVER: If a person does the research, speaks with a nutritionalist, and takes the time to actually make sure that the animal is getting the required nutrition, maybe. I haven't met an animal raised on such a diet, so I can't say for sure what my opinion is.

Veegan: Please show me documentation proving that such things are still used in meat-based pet foods. I can find plenty of information from several decades ago, but nothing current of the sort.